Vitamin A (all-trans-retinol) metabolism produces the hormone all-trans-retinoic acid. The long-term goals of this project include defining the molecular and endocrine aspects of the second reaction of retinoic acid biosynthesis, catalyzed by retinal dehydrogenase isozymes (RALDH). Substantial evidence suggests a model in which retinol and its metabolite all-trans- retinal bound to cellular retinol-binding protein, type I (CRBP) serve as substrates in the path of retinoic acid biosynthesis. Retinoids apparently travers through this pathway via a series of interactions between CRBP and enzymes that recognize the CRBP- retinoid complex. This project will continue to evaluate this model by identifying candidate RALDH and by testing the hypothesis that physiologically important isozymes of RALDH recognize retinal bound to CRBP as substrate. The specific aims are to: 1) clone cDNAs that encode candidate RALDH isozymes in addition to RALDH1 and RALDH2; 2) express these cDNAs in E. coli and establish the enzymatic characteristics of new enzymes, as well as RALDH1 and RALDH2; 3) determine temporal-spatial expression patterns of RALDH during development and aging, and as a function of dietary retinoid status; 4) isolate RALDH genomic clones and map the promoters; 5) produce and evaluate conditional and/or tissue-specific RALDH gene deleltion mice. This work aims to provide insight into the nature and regulation of RALDH and to generate reagents (antibodies, cDNA clones, knock-out mice) for in-depth study of endocrine, nutrition and aging effects on the conversion of retinal into retinoic acid. The fundamental insight and reagents generated ultimately will be used for identifying diseases and age-related degenerative processes that may be caused or exacerbated by impaired retinoic acid biosynthesis.